Photo mask, focus measuring method using the mask, and method of manufacturing semiconductor device

ABSTRACT

A photo mask includes an asymmetrical diffraction grating pattern in which diffraction efficiencies of plus primary diffracted light and minus primary diffracted light are different, the asymmetrical diffraction grating pattern including a shielding portion which shields light, a first transmitting portion which transmits light, and a second transmitting portion which transmits light, a ratio of widths of the shielding portion, the first transmitting portion, and the second transmitting portion being n11 where n is a positive real number except 2, the asymmetrical diffraction grating pattern approximately satisfying 163°≦360°/(n+2)+θ≦197° where θ (≠90°) indicates an absolute value of a difference between a phase of the light transmitted through the first transmitting portion and that of the light transmitted through the second transmitting portion, and a reference pattern for obtaining an image as a reference for measuring a shift of an image of the asymmetrical diffraction grating pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2004-217874, filed Jul. 26, 2004,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photo mask for use in a semiconductorfield, a focus measuring method using the mask, and a method ofmanufacturing a semiconductor device.

2. Description of the Related Art

A tolerance of focus permitted in lithography has been narrowed as adesign rule of a semiconductor device to be manufactured isminiaturized. When the tolerance of the focus is narrowed, flatness of awafer and specifications with respect to curvature of field of anexposure apparatus has been strict. Moreover, a high-precision measuringmethod of the focus, curvature of field and the like using a resistpattern transferred onto the wafer has become important.

A focus test mask comprising an asymmetrical diffraction grating patternand a reference pattern, and a focus measuring method using the focustest mask and utilizing a phenomenon in which an image of theasymmetrical diffraction grating pattern shifts in proportion to a focusvalue have been known (Jpn. Pat. No. 3297423). Since the focus measuringmethod has a high measurement precision having a measurement error of 5nm or less, and the measuring is simple, the method can be said to beone of most promising techniques at present.

The asymmetrical diffraction grating pattern comprises a shieldingportion, a transmitting portion, and 90° phase grooved portion. A linewidth ratio of the shielding portion, transmitting portion, and 90°phase grooved portion is ideally 2:1:1. On the other hand, analternating type phase shift exposure mask including a pattern (devicepattern) for manufacturing an actual semiconductor product comprises a180° phase grooved portion.

A method of manufacturing an exposure mask comprising the asymmetricaldiffraction grating pattern and the device pattern includes a step offorming the 90° phase grooved portion, and a step of forming the 180°phase grooved portion. When these two steps are performed, amanufacturing process is complicated, and manufacturing costs remarkablyrise. This respect will be further described hereinafter.

The step of forming the 180° phase grooved portion includes a step offorming a trench vertically in the surface of a quartz glass substrateby a dry process (e.g., a vertical etching process such as an RIEprocess); and a step of expanding the trench by predetermined amounts ina lateral direction and a vertical direction by a wet process (isotropicetching process). A sum of grooved amounts by the dry and wet processesis a grooved amount by which a phase of transmitted light delays by 180°as compared with a case where there is not any grooved portion.

To obtain a high-precision alternating type phase shift exposure mask,the groove has to be made vertically, and further expanded in thelateral direction. However, an etching process to expand the groove onlyin the lateral direction does not exist. Therefore, as described above,combined use of the dry and wet processes is required. Since an amountto be expanded in the lateral direction needs to be controlled with ahigh precision, the grooved amount in the dry process is a depthobtained by subtracting the amount to be expanded in the lateraldirection from the amount corresponding to 180°. On the other hand, toobtain a high-precision focus test mask, a grooved portion correspondingto 90° has to be formed only by the dry process.

Therefore, in a conventional technique, the above-described etchingprocesses have to be separately performed in order to realize thehigh-precision alternating type phase shift exposure mask and thehigh-precision focus test mask in one exposure mask, and a maskmanufacturing cost rises by at least 30% or more as compared with theconventional alternating type phase shift exposure mask.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided aphoto mask comprising: an asymmetrical diffraction grating pattern inwhich diffraction efficiencies of plus primary diffracted light andminus primary diffracted light are different, the asymmetricaldiffraction grating pattern including a shielding portion which shieldslight; a first transmitting portion which transmits light; and a secondtransmitting portion which transmits light, a ratio of widths of theshielding portion, the first transmitting portion, and the secondtransmitting portion being n:1:1 where n is a positive real numberexcept 2, the asymmetrical diffraction grating pattern approximatelysatisfying 163°≦360°/(n+2)+θ≦197° where θ (≠90°) indicates an absolutevalue of a difference between a phase of the light transmitted throughthe first transmitting portion and that of the light transmitted throughthe second transmitting portion; and a reference pattern configured toobtain an image as a reference for measuring a shift of an image of theasymmetrical diffraction grating pattern.

According to an aspect of the present invention, there is provided afocus measuring method comprising: preparing a focus test mask, thefocus test mask comprising: an asymmetrical diffraction grating patternin which diffraction efficiencies of plus primary diffracted light andminus primary diffracted light are different, the asymmetricaldiffraction grating pattern including a shielding portion which shieldslight, a first transmitting portion which transmits light, and a secondtransmitting portion which transmits light, a ratio of widths of theshielding portion, the first transmitting portion, and the secondtransmitting portion being n:1:1 where n is a positive real numberexcept 2, the asymmetrical diffraction grating pattern approximatelysatisfying 163°≦360°/(n+2)+θ≦197° where θ (≠90°) indicates an absolutevalue of a difference between a phase of the light transmitted throughthe first transmitting portion and that of the light transmitted throughthe second transmitting portion; and a reference pattern configured toobtain an image as a reference for measuring a shift of an image of theasymmetrical diffraction grating pattern; applying a photosensitiveagent on the substrate; exposing images of the asymmetrical diffractiongrating pattern and the reference pattern in the photo mask at the sametime onto the substrate; developing a pattern transferred on thesubstrate; and measuring a relative distance between the images of theasymmetrical diffraction grating pattern and the reference patternformed on the substrate.

According to an aspect of the present invention, there is provided amethod of manufacturing a semiconductor device comprising: preparing anexposure mask, the exposure mask comprising an asymmetrical diffractiongrating pattern in which diffraction efficiencies of plus primarydiffracted light and minus primary diffracted light are different, theasymmetrical diffraction grating pattern including a shielding portionwhich shields light, a first transmitting portion which transmits light,and a second transmitting portion which transmits light, a ratio ofwidths of the shielding portion, the first transmitting portion, and thesecond transmitting portion being n:1:1 where n is a positive realnumber except 2, the asymmetrical diffraction grating patternapproximately satisfying 163°≦360°/(n+2)+θ≦197° where θ (≠90°) indicatesan absolute value of a difference between a phase of the lighttransmitted through the first transmitting portion and that of the lighttransmitted through the second transmitting portion; a reference patternconfigured to obtain an image which is a reference in measuring a shiftof an image of the asymmetrical diffraction grating pattern; and adevice pattern; applying a photosensitive agent on the substrate;exposing images of the asymmetrical diffraction grating pattern, thereference pattern, and the device pattern in the photo mask at the sametime onto the substrate; developing a pattern transferred on thesubstrate; inspecting the device pattern formed on the substrate; andmeasuring a relative distance between the images of the asymmetricaldiffraction grating pattern and the reference pattern in a case where adefect is detected in the device pattern in the inspecting the devicepattern formed on the substrate.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a plan view schematically showing a photo mask (focus testmask) of an embodiment;

FIG. 2 is a plan view schematically showing another photo mask (exposuremask) of the embodiment;

FIG. 3 is a plan view showing details of a test mask of the embodiment;

FIG. 4 is a sectional view along arrows A-A′ of FIG. 3;

FIGS. 5A to 5H are sectional views showing a method of manufacturing theexposure mask of the embodiment;

FIG. 6 is a sectional view showing the exposure mask of the embodiment;

FIG. 7 is a diagram showing a relation between n and θ;

FIGS. 8A to 8F are sectional views of PSG patterns corresponding ton=0.5, 1.0, 1.5, 2.0, 2.5, 3.0;

FIGS. 9A to 9C are plan views showing test marks including typicalreference patterns;

FIGS. 10A to 10C are plan views showing test marks capable ofeliminating measurement errors attributed to a measuring apparatus;

FIGS. 11A to 11C are plan views showing another test marks capable ofeliminating the measurement errors attributed to the measuringapparatus;

FIG. 12 is a plan view showing a test mark capable of measuring focusand astigmatism;

FIGS. 13A to 13D are plan views showing test marks corresponding toautomatic measurements by an alignment shift inspection apparatus;

FIGS. 14A and 14B are sectional views along A-A′ and B-B′ of FIG. 13D;

FIGS. 15A and 15B are plan views of test marks capable of linearizing arelation between a focus value and a positional shift;

FIG. 16 is a plan view showing an exposure mask including the test markof FIG. 15;

FIG. 17 is an explanatory view of a double exposure method using theexposure mask of FIG. 16; and

FIG. 18 shows a test mark for measuring a focus based on a profile ofreflected light.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings.

FIGS. 1 and 2 are plan views schematically showing a photo mask of theembodiment. Concretely, FIG. 1 shows an example of a focus test maskPM1, and FIG. 2 shows an example of an exposure mask PM2.

The focus test mask PM1 comprises a quartz glass substrate 1, and a testmark TM for focus measurement, provided on the quartz glass substrate 1.

The exposure mask PM2 comprises the quartz glass substrate 1, the testmark TM provided on the quartz glass substrate 1, and an alternatingtype phase shift mask PSM provided on the quartz glass substrate 1 andincluding a pattern (device pattern) for manufacturing an actualsemiconductor product. The phase shift mask PSM comprises a shieldingportion, and first and second transmitting portions (phase groovedportions). An absolute value of a difference between phases of lightstransmitted through the first and second transmitting portions is 180°.

Each of the test marks TM in the focus test masks PM1, PM2 comprises anasymmetrical diffraction grating pattern (hereinafter referred to as thePSG pattern) 2 including a periodic pattern which differs in diffractionefficiency with plus and minus primary diffracted lights, and areference pattern 3.

FIG. 3 is a plan view showing details of the PSG pattern 2. FIG. 4 is asectional view along arrows A-A′ of FIG. 3.

The PSG pattern 2 comprises shielding portions 4 which are provided onthe glass substrate 1 and shield the light; the first transmittingportions 5 which are provided on the glass substrate 1 and transmit thelight; and the second transmitting portions 6 (phase grooved portions)which are provided on the glass substrate 1 and transmit the light.

The shielding portion 4, the first transmitting portion 5, and thesecond transmitting portion 6 satisfy the following two equations ([1],[2]).W1:W2:W3=n:1:1  [Equation 1]163°≦360°/(n+2)+θ≦197°  [Equation 2]

W1 . . . width of the shielding portion 4

W2 . . . width of the first transmitting portion 5

W3 . . . width of the second transmitting portion 6

n . . . positive real number other than 2

θ . . . absolute value of the difference between the phase of the lighttransmitted through the first transmitting portion 5 and that of thelight transmitted through the second transmitting portion 6.Additionally, 90° is excluded.

FIGS. 5A to 5H are sectional views showing a method of manufacturing theexposure mask PM2. A left side of a one-dot chain line shows a region(PSG region) occupied by the PSG pattern 2 in the mask, and a right sideof the one-dot chain line shows a region (alternating PSM region)occupied by the phase shift mask PSM in the mask.

First, as shown in FIG. 5A, a chromium film (shielding film) 4 to beprocessed into the shielding portion is formed on the quartz glasssubstrate 1.

Next, as shown in FIG. 5B, a resist film is formed on the chromium film4, and thereafter exposing and developing are performed with respect tothe resist film to form a resist pattern 11. The resist pattern 11 formsshielding portions in a PSG region and alternating PSM region. Theresist film is exposed, for example, by EB drawing.

Next, as shown in FIG. 5C, the chromium film 4 is etched using theresist pattern 11 a mask. As a result, the shielding portions 4comprising chromium are formed in the PSG region and alternating PSMregion. Thereafter, the resist pattern 11 is removed.

In the present embodiment, a step of forming the resist pattern forforming the shielding portion 4 in the PSG region, and a step of formingthe resist pattern for forming the shielding portion in the alternatingPSM region are simultaneously performed in the step of FIG. 5B.Furthermore, an etching step for forming the shielding portion 4 in thePSG region, and an etching step for forming the shielding portion in thealternating PSM region are simultaneously performed in the step of FIG.5C. Therefore, a manufacturing process of the exposure mask PM2 of thepresent embodiment is not changed as compared with the manufacturingprocess of a phase shift mask of a conventional alternating type.

It is to be noted that the step of forming the resist pattern forforming the shielding portion 4 in the PSG region, and the step offorming the resist pattern for forming the shielding portion in thealternating PSM region may be performed in separate steps, and theetching step for forming the shielding portion 4 in the PSG region andthe etching step for forming the shielding portion in the alternatingPSM region may be performed in separate steps.

In this case, the process of forming the shielding portion 4 in the PSGregion, and the process of forming the shielding portion in thealternating PSM region can be easily optimized. For example, the step offorming the resist pattern for forming the shielding portion 4 in thePSG region may be performed using a photo repeater which is a apparatushaving a higher alignment precision as compared with an EB exposureapparatus.

Next, as shown in FIG. 5D, a resist pattern 12 is formed on theshielding portions 4 and quartz glass substrate 1. The resist pattern 12forms the first and second transmitting portions (phase groovedportions) in the PSG and alternating PSM regions.

Next, as shown in FIG. 5E, the surface of the quartz glass substrate 1is etched by an RIE process (dry process) using the resist pattern 12 asa mask. As a result, a plurality of grooved portions (trenches) areformed in the surface of the quartz glass substrate 1. These groovedportions have substantially vertical side walls. FIG. 5E shows sevengrooved portions. Thereafter, the resist pattern 12 is removed.

Among the plurality of grooved portions, the grooved portions in the PSGregion form the second transmitting portions 6. Among the plurality ofgrooved portions, the grooved portions in the alternating PSM regionform the second transmitting portions through a wet process of FIG. 5G.

Moreover, portions in which any shielding portion 4 is not formed andany grooved portion is not formed form the first transmitting portions 5in the PSG region and the alternating PSM region.

Next, as shown in FIG. 5F, a resist pattern 13 is formed on theshielding portions 4 and the quartz glass substrate 1. The resistpattern 13 forms second transmitting portions (phase grooved portions)in the alternating PSM region. The PSG region is masked by the resistpattern 13. The alternating PSM region excluding the grooved portions ismasked by the resist pattern 13.

Next, as shown in FIG. 5G, the surface of the quartz glass substrate 1is etched by the wet process using the resist pattern 13 as a mask, andthe grooved portions in the alternating PSM region are expanded in thelateral and vertical directions. The grooved portions expanded in thelateral and vertical directions form second transmitting portions 6′ inthe alternating PSM region.

Thereafter, as shown in FIG. 5H, the resist pattern 13 is removed, andthe exposure mask PM2 is obtained.

FIG. 6 shows a sectional view of the exposure mask PM2 to which concretedimensional values are attached.

A depth of the grooved portion of the second transmitting portion 6′ isstrictly controlled in such a manner that the absolute value of thedifference between the phase of the light transmitted through the firsttransmitting portion 5 in the alternating PSM region and that of thelight transmitted through the second transmitting portion 6′ is 180°.

The depth of the grooved portion of the second transmitting portion 6′having a depth corresponding to 180° described above can be formed onlyby the RIE process without using any wet process. However, the groovedportion of the second transmitting portion 6′ is formed using the RIEand wet processes for the following reasons.

Reaction products generated in the RIE process of FIG. 5E adhere to theside walls of the grooved portions. When the reaction products adhere tothe side walls of the grooved portions, light transmission intensity ofthe grooved portion is reduced as compared with a non-grooved opening(surface portion of the quartz glass substrate 1 coated with the resistpattern 12). The reduction of the light transmission intensity of thegrooved portion causes a dimensional error of the resist pattern formedon the wafer.

Then, after the RIE process, by performing the wet process, the reactionproducts adhering to the side walls of the grooved portions is removedand the grooved portion of the second transmitting portion 6′ having thedepth corresponding to 180° described above is formed.

A total etching amount in the RIE and wet processes needs to be set toan amount corresponding to 180° described above.

In this case, distribution of the etching amounts in a depth direction(vertical direction) in the RIE process and in a depth direction(vertical direction) in the wet process is determined in considerationof a side etching amount (etching amount in the lateral direction,required for removing the reaction products) required in the wetprocess.

Generally, an etching amount corresponding to 75° is selected in the RIEprocess of FIG. 5E, and an etching amount corresponding to 105° isselected in the wet process of FIG. 5E. In this case, the depth of thegrooved portion of the second transmitting portion 6′ in the PSG regionis a depth corresponding to 75°.

In the case of W1:W2:W3=n:1:1, the condition that one of plus primarydiffracted light and minus primary diffracted light turns to be vanishedis represented by the following equation.360°/(n+2)+θ=180°  [Equation 3]

When θ=75° is substituted into [Equation 3], n=1.4286. A line widthratio (W1:W2:W3) of the PSG pattern is designed beforehand at 1.43:1:1.

That is, the line width ratio of the PSG pattern is selected in such amanner that the etching of the quartz glass substrate 1 for forming thePSG pattern is performed only by the RIE process without using any wetprocess. Therefore, a test mark having a high dimensional precision ismanufactured.

Furthermore, the method of manufacturing the exposure mask PM2 of thepresent embodiment is the same as the conventional method ofmanufacturing an exposure mask except the pattern layout (shape anddimension of the pattern) on the quartz glass substrate 1.

Therefore, according to the present embodiment, it is possible to easilyrealize the exposure mask including the device pattern and the test markhaving the high precision without incurring any increase of themanufacturing cost.

Moreover, when the device pattern is omitted from the exposure mask, itis possible to easily realize a focus test mark including high precisiontest mark without incurring any increase of manufacturing cost.

FIG. 7 shows a relation between n and θ in the case of W1:W2:W3=n:1:1.

In FIG. 7, c denotes a ratio (light intensity ratio) of an intensity ofthe plus primary diffracted light to that of the minus primarydiffracted light. The primary diffracted light having a higher intensityis selected for a denominator of the light intensity ratio.

A thick solid line shows ε=0. A curve of ε=0 shows a relation between nand θ in a case where one primary diffracted light completely vanishesε=0.01 (ideal condition).

On the other hand, two thin solid lines show ε=0.01. A curve of ε=0.01shows a relation between n and θ in a case where one primary diffractedlight has an intensity of about 1% of that of the other diffractedlight.

Moreover, two dotted lines show ε=0.02. A curve of ε=0.02 shows arelation between n and θ in a case where one primary diffracted lighthas an intensity of about 2% of that of the other diffracted light. In aregion held between these two dotted lines, focus measuring issufficiently correctly performed. This region is represented by[Equation 2] described above.

Here, Table 1 shows a relation between n and θ (ideal value, effectiverange) in the case of ε=0.02. TABLE 1 θ Ideal Effective n value range0.5 36° 19 to 53° 1.0 60° 43 to 77° 1.5 77.143°    60 to 94° 2.0 90° 73to 107° 2.5 100°  83 to 117° 3.0 108°  91 to 125°

As θ is closer to the ideal value, needless to say, a focus measurementprecision becomes higher. However, when ease of designing of the mask isconsidered, n is preferably a definite number (round number). FIGS. 8Ato 8F show sectional views of PSG patterns corresponding to n=0.5(θ=36°), 1.0 (θ=60°), 1.5 (θ=77.143°), 2.0 (θ=90°), 2.5 (θ=100°), 3.0(θ=108°). Especially, the mask of FIG. 8D is a mask comprising astructure described as one example in Jpn. Pat. No. 3297423. Maskshaving realistic θ and n are the masks shown in FIGS. 8A, 8B, and 8F.

The focus test mask PM1 of the present embodiment will be describedfurther. As described above, the focus test mask PM1 of the presentembodiment comprises the test mark TM and the reference pattern 3.

As the reference pattern 3, mainly there are three types shown in FIGS.9A to 9C. That is, there are a large isolated pattern 3 a shown in FIG.9A, a diffraction grating pattern 3 b shown in FIG. 9B, and anasymmetrical diffraction grating 3 c whose direction is opposite to thatof the PSG pattern 2 as shown in FIG. 9C.

Since the large isolated pattern 3 a has a broad DOF, the measuringhaving a broad focus range is possible. Since an influence of comaaberration of the diffraction grating pattern 3 b is equivalent to thatof an asymmetrical diffraction grating, the measuring which is notinfluenced by the coma aberration is possible. Moreover, since arelative shift amount of the opposite directed asymmetrical diffractiongrating 3 c is double, the measuring having twice sensitivity ispossible.

Moreover, to remove the measurement error attributed to the measuringapparatus, as shown in FIGS. 10A to 10C and 11A to 11C, it is preferableto use the test mark TM having a structure in which one PSG pattern 2 isput between two reference patterns (two large isolated patterns 3 a, twodiffraction grating patterns 3 b, or two asymmetrical diffractiongratings 3 c). Conversely, even when using a structure in which onereference pattern is put between two PSG patterns, similarly themeasurement error attributed to the measuring apparatus can be removed.It is to be noted that in FIG. 10 and subsequent figures, patterns arenot necessarily denoted with reference numerals for simplicity, and thesame hatching shows the same portion.

Furthermore, when astigmatism exists in a projection lens, as shown inFIG. 12, by the use of the test mark TM having a structure in which PSGpatterns 2 in two directions crossing each other at right angles aredisposed in the vicinity of each other, not only the focus but also theastigmatism can be measured.

FIG. 13 show plan views showing test marks corresponding to automaticmeasurements by an alignment shift inspection apparatus. FIG. 14 showsectional views along arrows A-A′ and B-B′ of FIG. 13D.

A test mark TM shown in FIG. 13A includes two asymmetrical diffractiongrating patterns 2 (the first and second asymmetrical diffractiongrating patterns), and two reference patterns (the first and secondreference patterns) 3 a.

In a test mark TM shown in FIG. 13B, reference patterns 3 a in the testmark TM shown in FIG. 13A is replaced with reference patterns 3 b.

In a test mark TM shown in FIG. 13C, reference patterns 3 a in the testmark TM shown in FIG. 13A is replaced with reference patterns 3 c.

A test mark TM shown in FIG. 13D comprises a rectangular test mark TM1,and a rectangular test mark TM2 provided in such a manner as to surroundthe test mark TM1. The test marks TM1, TM2 are test marks obtained bychanging a linear test mark obtained by vertically extending the testmark of one of FIGS. 13A to 13C into a rectangular shape.

That is, the test mark TM shown in FIG. 13D includes the first andsecond asymmetrical diffraction grating patterns and the first andsecond reference patterns, the first asymmetrical diffraction gratingpattern and the first reference pattern are disposed in parallel on thefirst line, and the second asymmetrical diffraction grating pattern andthe second reference pattern are disposed in parallel on the second linevertical to the first line.

In the test marks of FIGS. 13A to 13D, a relation between a focus valueand a positional shift is not linear.

Examples of a test mark which improve the situation include test marksshown in FIGS. 15A and 15B. Exposure is performed using a test mark TMashown in FIG. 15A, and thereafter the exposure is performed using a testmark TMb shown in FIG. 15B. Measurement patterns formed by theseexposures have advantages that a relation between the focus value andthe positional shift is substantially linear.

FIG. 16 is a plan view showing an exposure mask including the test marksTMa, TMb. The test marks TMa, TMb are arranged in a peripheral portionof an exposure region of an exposure mask.

FIG. 17 is an explanatory view of a double exposure method using theexposure mask of FIG. 16. In this method, the double exposure isperformed utilizing an overlap region 24 of exposure regions 22, 23adjacent to each other on a wafer 21.

That is, two exposure steps for two adjacent exposure regions 22, 23 areperformed in such a manner that the pattern of the test mark TMatransferred in the exposure region 22 and the pattern of the test markTMb transferred in the exposure region 23 overlap each other in apredetermined manner in the overlapped region 24. Accordingly, twoexposure steps for performing the double exposure of the test marks donot have to be separately added.

FIG. 18 shows a plan view of the test mark for measuring a focus basedon a profile of reflected light.

The test mark of FIG. 18 includes a plurality of asymmetricaldiffraction grating patterns 2 and a plurality of reference patterns 3.The asymmetrical diffraction grating patterns 2 and the referencepatterns 3 are arranged in parallel on a line, and shifted in a lateraldirection by a certain amount, while the asymmetrical diffractiongrating patterns 2 and the reference patterns 3 are alternately arrangedin a vertical direction.

In the configuration, since the patterns alternately shift in a verticaldirection by the focus, the profile of the reflected light changes byinterference by the shift. A focus value can be measured from the changeof the profile. The profile of the reflected light can be acquired, forexample, using a device referred to as a scatterometoroy. When the testmark of FIG. 18 is used, there is an advantage that the double exposureis not required.

A focus measuring method of the present embodiment is as follows.

In the focus measuring method of the present embodiment, a projectionexposure apparatus is used which projects an image of a mask patternformed on a photo mask onto a substrate via an optical projectionsystem. The image of the test mark formed on the photo mask (focus testmask) of the present embodiment is projected onto the substrate usingthe projection exposure apparatus, and a defocus amount on the surfaceof the substrate is acquired using the image.

In further detail, at first, a photosensitive agent is applied on thesubstrate.

Next, images of the diffraction grating pattern and reference pattern inthe test mark in the photo mask are exposed at the same time on thesubstrate.

Next, the pattern transferred onto the substrate is developed.

Next, a relative distance between the images of the diffraction gratingpattern and the reference pattern formed on the substrate is measured,and the defocus amount is acquired based on the measured distance.

A method of manufacturing a semiconductor device of the presentembodiment is as follows.

In the method of manufacturing the semiconductor device of the presentembodiment, the projection exposure apparatus which projects the imageof the mask pattern formed on the exposure mask onto the substrate viathe optical projection system is used. The images of the device patternand the test mark formed on the photo mask (exposure mask) of theembodiment are projected onto the substrate using the projectionexposure apparatus, an actual semiconductor product is manufacturedusing the images, and the defocus amount of the surface of the substrateis acquired. Various combinations of the phase shift mask PSM of theexposure mask of the embodiment and the test mark TM are considered, andany combination may be used.

In further detail, at first, a photosensitive agent is applied on thesubstrate.

Next, the images of the asymmetrical diffraction grating pattern,reference pattern, and device pattern in the photo mask are exposed onthe substrate at the same time.

Next, the pattern transferred on the substrate is developed.

Next, the device pattern formed on the substrate is inspected.

Next, when a defect is detected in the device pattern formed on thesubstrate in a step of inspecting the device pattern, the relativedistance between the images of the diffraction grating pattern and thereference pattern is measured, and the defocus amount is acquired basedon the measured distance.

Next, the device pattern in which the defect is detected, and thedefocus amount are recorded in a memory device. A type of the memorydevice is not especially limited.

Next, the photo mask related to the device pattern in which the defectis detected is corrected.

Here, a case where the defocus amount is acquired when the defect isdetected has been described, but the defocus amount may be acquiredirrespective of presence of detection of the defect.

By constructing a database of a wafer history including the devicepattern and the defocus amount, a cause for an inadvertently generatedyield reduction can be easily investigated, and the reduction of theyield can be prevented beforehand.

Examples of the semiconductor device include a liquid crystal display(LCD) and devices using LCD (e.g., a cellular phone, liquid crystaltelevision, personal computer, PDA) in addition to a DRAM, logic LSI,and system LSI (DRAM embedded LSI).

As described above, the photo mask in which the line width ratio of theshielding portion, transmitting portion, and phase grooved portion is2:1:1 and a phase difference between the lights transmitted through thetransmitting portion and the phase grooved portion is 90° is a mostideal photo mask for focus measuring. However, even by the use of thephoto mask of the embodiment in which the phase difference and the linewidth ratio satisfy [Equation 2] instead of the above-described idealphoto mask, the high precision focus measuring substantially similar tothat by the ideal photo mask is possible. Accordingly, for example, evenwhen the asymmetrical diffraction grating is formed on a usualalternating type phase shift mask, a grooved amount can be set withrespect to the phase difference having few loads on the maskmanufacturing, and a high precision focus measuring technique equivalentto a conventional technique can be realized even in various exposuremasks.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A photo mask comprising: an asymmetrical diffraction grating patternin which diffraction efficiencies of plus primary diffracted light andminus primary diffracted light are different, the asymmetricaldiffraction grating pattern including a shielding portion which shieldslight; a first transmitting portion which transmits light; and a secondtransmitting portion which transmits light, a ratio of widths of theshielding portion, the first transmitting portion, and the secondtransmitting portion being n:1:1 where n is a positive real numberexcept 2, the asymmetrical diffraction grating pattern approximatelysatisfying 163°≦360°/(n+2)+θ≦197° where θ (≠90°) indicates an absolutevalue of a difference between a phase of the light transmitted throughthe first transmitting portion and that of the light transmitted throughthe second transmitting portion; and a reference pattern configured toobtain an image as a reference for measuring a shift of an image of theasymmetrical diffraction grating pattern.
 2. The photo mask according toclaim 1, wherein the reference pattern is an asymmetrical diffractiongrating pattern symmetrical to the asymmetrical diffraction gratingpattern.
 3. The photo mask according to claim 1, wherein the referencepattern includes first and second reference patterns, and theasymmetrical diffraction grating pattern is disposed between the firstand second reference patterns.
 4. The photo mask according to claim 1,wherein the asymmetrical diffraction grating pattern includes first andsecond asymmetrical diffraction grating patterns, and the referencepattern is disposed between the first and second asymmetricaldiffraction grating patterns.
 5. The photo mask according to claim 1,wherein the asymmetrical diffraction grating pattern includes first andsecond asymmetrical diffraction grating patterns, the reference patternincludes first and second reference patterns, the first asymmetricaldiffraction grating pattern and the first reference pattern are arrangedin parallel on a first line, and the second asymmetrical diffractiongrating pattern and the second reference pattern are arranged inparallel on a second line vertical to the first line.
 6. The photo maskaccording to claim 1, wherein the asymmetrical diffraction gratingpattern includes a plurality of asymmetrical diffraction gratingpatterns, the reference pattern includes a plurality of referencepatterns, and the plurality of asymmetrical diffraction grating patternsand the plurality of reference patterns are arranged in parallel on aline, and alternately arranged.
 7. The photo mask according to claim 1,wherein the θ and the n approximately satisfy 360°/(n+2)+θ=180°.
 8. Thephoto mask according to claim 1, wherein the θ is approximately 36°, andthe n is approximately 0.5.
 9. The photo mask according to claim 1,wherein the θ is approximately 60°, and the n is approximately
 1. 10.The photo mask according to claim 1, wherein the θ is approximately108°, and the n is approximately
 3. 11. The photo mask according toclaim 1, further comprising: a device pattern.
 12. The photo maskaccording to claim 2, further comprising: a device pattern.
 13. A focusmeasuring method comprising: preparing a focus test mask, the focus testmask comprising: an asymmetrical diffraction grating pattern in whichdiffraction efficiencies of plus primary diffracted light and minusprimary diffracted light are different, the asymmetrical diffractiongrating pattern including a shielding portion which shields light, afirst transmitting portion which transmits light, and a secondtransmitting portion which transmits light, a ratio of widths of theshielding portion, the first transmitting portion, and the secondtransmitting portion being n:1:1 where n is a positive real numberexcept 2, the asymmetrical diffraction grating pattern approximatelysatisfying 163°≦360°/(n+2)+θ≦197° where θ (≠90°) indicates an absolutevalue of a difference between a phase of the light transmitted throughthe first transmitting portion and that of the light transmitted throughthe second transmitting portion; and a reference pattern configured toobtain an image as a reference for measuring a shift of an image of theasymmetrical diffraction grating pattern; applying a photosensitiveagent on the substrate; exposing images of the asymmetrical diffractiongrating pattern and the reference pattern in the photo mask at the sametime onto the substrate; developing a pattern transferred on thesubstrate; and measuring a relative distance between the images of theasymmetrical diffraction grating pattern and the reference patternformed on the substrate.
 14. The focus measuring method according toclaim 13, wherein the reference pattern is an asymmetrical diffractiongrating pattern symmetrical to the asymmetrical diffraction gratingpattern.
 15. The focus measuring method according to claim 13, whereinthe reference pattern includes first and second reference patterns, andthe asymmetrical diffraction grating pattern is disposed between thefirst and second reference patterns.
 16. The focus measuring methodaccording to claim 13, wherein the asymmetrical diffraction gratingpattern includes first and second asymmetrical diffraction gratingpatterns, and the reference pattern is disposed between the first andsecond asymmetrical diffraction grating patterns.
 17. The focusmeasuring method according to claim 13, wherein the asymmetricaldiffraction grating pattern includes first and second asymmetricaldiffraction grating patterns, the reference pattern includes first andsecond reference patterns, the first asymmetrical diffraction gratingpattern and the first reference pattern are arranged in parallel on afirst line, and the second asymmetrical diffraction grating pattern andthe second reference pattern are arranged in parallel on a second linevertical to the first line.
 18. The focus measuring method according toclaim 13, wherein the asymmetrical diffraction grating pattern includesa plurality of asymmetrical diffraction grating patterns, the referencepattern includes a plurality of reference patterns, and the plurality ofasymmetrical diffraction grating pattern and plurality of the referencepattern are arranged in parallel on a line, and alternately arranged.19. The focus measuring method according to claim 13, wherein the θ andthe n approximately satisfy 360°/(n+2)+θ=180°.
 20. A method ofmanufacturing a semiconductor device comprising: preparing an exposuremask, the exposure mask comprising an asymmetrical diffraction gratingpattern in which diffraction efficiencies of plus primary diffractedlight and minus primary diffracted light are different, the asymmetricaldiffraction grating pattern including a shielding portion which shieldslight, a first transmitting portion which transmits light, and a secondtransmitting portion which transmits light, a ratio of widths of theshielding portion, the first transmitting portion, and the secondtransmitting portion being n:1:1 where n is a positive real numberexcept 2, the asymmetrical diffraction grating pattern approximatelysatisfying 163°≦360°/(n+2)+θ≦197° where θ (≠90°) indicates an absolutevalue of a difference between a phase of the light transmitted throughthe first transmitting portion and that of the light transmitted throughthe second transmitting portion; a reference pattern configured toobtain an image which is a reference in measuring a shift of an image ofthe asymmetrical diffraction grating pattern; and a device pattern;applying a photosensitive agent on the substrate; exposing images of theasymmetrical diffraction grating pattern, the reference pattern, and thedevice pattern in the photo mask at the same time onto the substrate;developing a pattern transferred on the substrate; inspecting the devicepattern formed on the substrate; and measuring a relative distancebetween the images of the asymmetrical diffraction grating pattern andthe reference pattern in a case where a defect is detected in the devicepattern in the inspecting the device pattern formed on the substrate.